Study On Nitrogen And Phosphorus Removal Performance Of Corncob / Sponge Iron Composite Filler For Low C/N Wastewater

In order to solve the problem of poor removal effect of nitrogen and phosphorus in the secondary effluent of urban sewage treatment plant,the combined filler of corncob/sponge iron was used as the external carbon source and microbial carrier of sequencing batch biofilm reactor（Sequencing Biofilm Batch Reactor,SBBR）to improve the effect of nitrogen and phosphorus removal of low C/N wastewater.Explore the performance of corncob and straw as slow-release carbon source under different modified conditions,and select the best slow-release carbon source material to treat low C/N wastewater;The operation characteristics of SBBR reactor with modified corncob as slow-release carbon source were studied,and the optimal dosage of sponge iron enhanced bioreactor was determined;The effects of different hydraulic retention time（HRT）,dissolved oxygen concentration（DO）and temperature on the nitrogen and phosphorus removal performance of corn cob/sponge iron enhanced SBBR reactor were investigated.The corncob and straw was dried and washed by 1.5%Na OH alkali treatment,1.5%H₂O₂oxidation treatment and solution alkali oxidation treatment containing 1.5%Na OH and1.5%H₂O₂at the same time.The changes of the quality and surface structure of the solid carbon source before and after treatment were observed.The release law of COD,NH₄⁺-N,TN and TP and the value of m（BOD₅）/m（COD）in the leaching solution were continuously determined through static experiment.Among them,the solid carbon source treated with 1.5%Na OH solution has coarser surface and more pores,which is suitable for microbial growth and reproduction,high biochemical performance,good and lasting carbon release capacity,and the release of nitrogen and phosphorus is almost negligible.After screening,the corncob treated with 1.5%Na OH solution is more suitable as a solid slow-release carbon source for nitrogen and phosphorus removal of low C/N wastewater.The activated sludge in the reactor was acclimated for 60 days to adapt to the low-carbon environment with C/N of 2.The corncob material treated with 1.5%Na OH solution was added into the reactor as a slow-release carbon source.The treatment efficiency of NH₄⁺-N,TN and TP was significantly improved,and the effluent concentration was reduced to8.33mg/L,19.21mg/L and 0.52mg/L.Compared with the slow-release carbon source without corncob,the removal rate was increased by 24.41%,16.04%and 15.43%respectively,It shows that the system has a strong ability to remove pollutants.Sponge iron and alkaline corncob combined filler are added into SBBR reactor together.When the dosage of sponge iron is 40mg/L,the nitrogen and phosphorus removal performance of the system is significantly enhanced compared with other dosage.At this time,the removal rates of NH₄⁺-N,TN and TP are 75.63%,65.56%and 88.36%.Under this dosage,the nitrogen and phosphorus removal performance of the system is the best.Therefore,it is determined that the optimal dosage of sponge iron is 40mg/L.The effects of three factors such as hydraulic retention time（HRT）,dissolved oxygen concentration（DO）and temperature on the nitrogen and phosphorus removal effect of SBBR reactor were studied.It was finally determined that when the hydraulic retention time（HRT）was 8h,the dissolved oxygen concentration（DO）was3.5mg/L and the temperature was 15℃,the operation effect of the reactor was the best.Due to the diversity of microbial population in the system,the effluent effect of the system under different operating conditions is different,but under the appropriate operating conditions of the system,it has a good removal effect on NH₄⁺-N,TN and TP in the reactor,and the removal capacity of the reactor is improved,so the optimal operating conditions of SBBR reactor are determined.The corn cob/sponge iron combined filler was added into the SBBR reactor and operated according to the known best working conditions to investigate the nitrogen and phosphorus removal performance of the reactor.After 20 days of stable operation of the system,the average effluent concentrations of COD,NH₄⁺-N,TN and TP are 25.52mg/L,3.68mg/L,12.32mg/L and 0.36mg/L respectively,and the average removal rates are 74.5%,89.43%,73.71%and 88.21%respectively,meeting the effluent standard of class I a standard of pollutant discharge standard of urban sewage plant（GB18918）.